First time star formation seen in such extreme conditions

Astronomers have for the first time found stars forming within the violent outflows of material ejected from a supermassive black hole at the center of a galaxy.

Stars are born under extreme conditions. Intense gravitational forces cause gas to collapse into a heated ball, until the pressure can be balanced with the outward radiation force generated as the star begins to shine. A paper published in Nature today shows that these conditions can exist around a black hole and can support star formation.

Active galaxies shoot powerful jets of energy from their centers, where a hungry black hole is gobbling surrounding material.

Angular momentum causes the falling gas and dust to be whisked into a frenzy around the void, causing it to pool into a disc – also known as an accretion disc. The gravitational tug and frictional forces heat the accretion disc and powerful beams of energy are ejected.

“Astronomers have thought for a while that conditions within these outflows could be right for star formation, but no one has seen it actually happening, as it’s a very difficult observation,” said Roberto Maiolino, leader of the study and professor of experimental astrophysics at University of Cambridge, UK.

“Our results are exciting because they show unambiguously that stars are being created inside these outflows.”

Using spectroscopy instruments aboard the European Southern Observatory’s Very Large Telescope, the researchers were able to pinpoint the radiation released from a stellar nursery growing at the core of the IRAS F23128 galaxy.

IRAS F23128-5919 is actually made up of two galaxies colliding together. Energy emitted from young stars lights up nearby gas clouds, making them glow in a particular way. The light can be studied using a spectroscope to identify the source.

The fast motion and velocity of these stars provide further proof that they are locked within the powerful, hot winds emitted from the black hole.

“The stars that form in the wind close to the galaxy center might slow down and even start heading back inwards, but the stars that form further out in the flow experience less deceleration and can even fly off out of the galaxy altogether,” said Helen Russell, co-author of the paper and astronomer at the University of Cambridge.

First impressions show that the stars detected within the powerful, hot winds ejected around the black hole are brighter and hotter than stars formed in less extreme environments. They are estimated to be less than a few tens of millions of years old.

“If star formation is really occurring in most galactic outflows, as some theories predict, then this would provide a completely new scenario for our understanding of galaxy evolution,” said Maiolino.

The discovery could help astronomers understand how galaxies are shaped, how heavy elements are dispersed, and why the cosmic background radiation is irregular in some areas. ®